This application relates to the art of air brake systems and, more particularly, to air brake systems which include parking brakes.
Vehicles having front and rear axles have been provided with both service and parking brakes for the wheels on the front and rear axles. In order to provide controlled braking in the event of a failure in the service brakes, a known system provides a visual or audible signal to the operator who can then manually operate the parking brakes with a separate control. A system of this type is very awkward and it would be more desirable to have a system wherein the parking brakes would be automatically applied by operation of the service brake control in the event of a failure in the service brakes. A known system of that type is provided for vehicles having parking brakes only on the wheels mounted on the rear axle of the vehicle. Therefore, a failure in the service brakes for the wheels on the front axle results in the complete loss of braking force for the wheels on the front axle.